For example, in the architecture such as buildings, there are air-conditioning systems configured to control a plurality of indoor units, each of which is installed indoors and adjust the room temperature to an instructed temperature, and a plurality of outdoor units, each of which is installed outdoors and exhaust heat, with a centralized control apparatus. At this time, the outdoor units, the indoor units, and the centralized control apparatus are connected by transmission lines or the like to constitute a network. For example, each of the units or the apparatus transmits various signals including control data such as (operation on/off signals, set temperature differences, and operation modes), and performs communication.
Conventionally, in the air-conditioning systems, for example, the centralized control apparatus and each of the outdoor units are connected by transmission lines. The centralized control apparatus is further connected to indoor units, each linked to a corresponding one of the outdoor units by piping, by a repeater included in each of the outdoor units. In such a manner, a large network is often constructed with bus connection. Thus, if one of the units or apparatus that is connected to the network attempts to transmit a signal to another unit or apparatus, the signal is transmitted to all of the units and the apparatus. One signal occupies the entire network of the air-conditioning system (each of the units or the apparatus determines whether the signal is transmitted thereto, and the unit or the apparatus that has determined that the signal is transmitted thereto performs processing based on the signal). Accordingly, if the number of connected units is increased, or if signals are exchanged more frequently using a more advanced management system, traffic of signals transmitted over the network increases. If the traffic becomes saturated and the network occupied state continues, units unable to transmit a signal may emerge, for example. For this reason, for example, the centralized control apparatus cannot perform an effective management on the units or the room temperature adjustment.
Accordingly, for example, there is an air-conditioning system having a network configuration in which one or more networks, which are constituted by connecting one or more indoor units by transmission lines, are connected to a network, which are constituted by connecting a centralized control apparatus and each of outdoor units by a transmission line, through a bridge (see, for example, Patent Document 1). The network configuration in this air-conditioning system is designed to resolve heavy traffic over the network in the system by preventing unnecessary signals from being transmitted to other networks. In addition, by configuring the network in such a manner, communication can be performed at a communication speed suitable for a small networking environment. For example, a communication speed over the transmission line interconnecting the centralized control apparatus and each of the outdoor units may be increased.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-316995